This invention relates to methods for making metal cyanide catalysts complexes and to methods for polymerizing alkylene oxides in the presence of a metal cyanide catalyst.
Polyethers are prepared in large commercial quantities through the polymerization of alkylene oxides such as propylene oxide and ethylene oxide. This polymerization reaction is usually conducted in the presence of an initiator compound and a catalyst. The initiator compound usually determines the functionality (number of hydroxyl groups per molecule of the polymer) and in some instances imparts some desired functionality. The catalyst is used to provide an economical rate of polymerization.
Metal cyanide complexes are becoming increasingly important alkylene oxide polymerization catalysts. These complexes are often referred to as xe2x80x9cdouble metal cyanidexe2x80x9d or xe2x80x9cDMCxe2x80x9d catalysts, and are the subject of a number of patents, including, for example, U.S. Pat. Nos. 3,278,457, 3,278,458, 3,278,459, 3,404,109, 3,427,256, 3,427,334, 3,427,335 and 5,470,813, among many others. In some instances, these complexes provide the benefit of fast polymerization rates and narrow polydispersities. Additionally, these catalysts are associated with the production of polyethers having very low levels of monofunctional unsaturated compounds.
Development efforts have focussed mainly on one specific metal cyanide catalyst complex, zinc hexacyanocobaltate, complexed with a specific complexing agent, t-butanol. The catalyst is typically prepared in a multistep process. First, separate solutions of zinc chloride and potassium hexacyanocobaltate are prepared. These solutions are then mixed together, followed immediately by adding a mixture of water and the complexing agent, t-butanol. A catalyst complex precipitates and is recovered and washed multiple times with mixtures of water and t-butanol. This washing process removes unwanted occluded ions, particular potassium and chlorine, and contributes the complexing agent to the structure of the catalyst complex. Often, a polyether polyol is included in one or more of these washings. Finally, the catalyst complex is dried and ground. It is then mixed with an initiator compound and an alkylene oxide to prepare the desired polyether.
The process just described is complex, requiring several washing steps. It also requires that excesses of water and t-butanol be used. The t-butanol complexing agent itself causes the complex to be difficult to handle. Often, a polyether polyol must be added to facilitate easy handling of the catalyst complex.
Thus, it would be desirable to provide a less expensive, more convenient method for preparing a metal cyanide catalyst complex and a simple method for using such catalyst complexes.
In one aspect, this invention is a method for preparing an active metal cyanide catalyst, comprising
(I) mixing;
a) a solution or dispersion of a metal cyanide compound in a first inert organic compound or mixture thereof, wherein the metal cyanide compound is represented by the general formula Hw[M1(CN)r(X)t] wherein
M1 is a transition metal ion;
each X represents a group other than cyanide that coordinates with the M1 ion; r is from 4 to 6, t is from 0-2, and w represents the absolute value of the valence of the M1(CN)r(X)tgroup; and
b) a solution or dispersion of a metal salt in a second inert organic compound or mixture thereof, wherein the metal salt is represented by the general formula MxAy wherein M is a metal ion that forms an insoluble precipitate with the metal cyanide grouping M1(CN)r(X)t, A represents an anion, and x and y are integers that balance the charges in the metal salt, and said second inert organic compound is the same as or miscible with said first inert organic compound or mixture thereof, said mixing being performed under conditions such that a precipitate forms and is suspended in said first and second inert organic compounds;
(II) dispersing the resulting mixture in an initiator compound, and
(III) removing said first inert organic compound or mixture and said second inert organic compound or mixture from the resulting dispersion.
This method provides a convenient way to make metal cyanide catalysts as fine dispersions in an initiator compound. Preferably, no separate organic complexing agent compound is present in the preparation, so that the costs associated with the use of the complexing agent are eliminated. In this process, multiple process steps, particularly catalyst washings, are eliminated. Costs associated with drying the catalyst complex and handling solids are also reduced or eliminated.
In a second aspect, this invention is a method for preparing an active metal cyanide catalyst, comprising
(I) mixing;
a) a first solution or dispersion of a metal cyanide compound in an initiator compound or mixture thereof, wherein the metal cyanide compound is represented by the general formula Hw[M1(CN)r(X)t] wherein
M1 is a transition metal ion;
each X represents a group other than cyanide that coordinates with the M1 ion; r is from 4 to 6, t is from 0-2, and w represents the absolute value of the valence of the M1(CN)r(X)t group; and
b) a second solution or dispersion of a metal salt in said initiator compound or mixture thereof, wherein the metal salt is represented by the general formula MxAy wherein M is a metal ion that forms an insoluble precipitate with the metal cyanide grouping M1(CN)r(X)t, A represents an anion, and x and y are integers that balance the charges in the metal salt,
xe2x80x83said mixing being performed under conditions such that a precipitate forms and is suspended in said initiator compound or mixture thereof
In a third aspect, this invention is a process wherein a dispersion of the first or second aspect is mixed with an alkylene oxide and the resulting mixture subjected to conditions sufficient to polymerize the alkylene oxide to form a poly(alkylene oxide) based on said initiator compound.
In the first aspect of the invention, a solution or dispersion of a metal compound in an organic compound is mixed with a solution or dispersion of a metal salt in an organic compound. The metal compound is represented by the general formula Hw[M1(CN)r(X)t], in which M1, X, r, t and w are as described before.
M1 is preferably Fe+3, Fe30 2, Co+3, Co+2, Cr+2, Cr+3, Mn+2, Mn+3, Ir+3, Ni+2, Rh+3, Ru+2, V+4 and V+5. Among the foregoing, those in the plus-three oxidation state are more preferred. Co+3 and Fe+3 are even more preferred and Co+3 is most preferred.
Preferred groups X include anions such as halide (especially chloride), hydroxide, sulfate, carbonate, oxalate, thiocyanate, isocyanate, isothiocyanate, C1-4 carboxylate and nitrite (NO2xe2x80x94), and uncharged species such as CO, H2O and NO. Particularly preferred groups X are NO, NO2xe2x80x94 and CO.
r is preferably 5 or 6, most preferably 6; t is preferably 0 or 1, most preferably 0. w is usually 2 or 3, and is most typically 3. In most cases, r+t will equal six.
Mixtures of two or more metal cyanide compounds can be used. In addition, the solution may also contain compounds that have the structure HwM2(X)6, wherein M2 is a transition metal and X is as before. M2 may be the same as or different from M1. The X groups in any M2(X)6 do not have to be all the same.
The organic compound is one that meets several requirements. First, it is inert to the metal cyanide compound and any HwM2(X)6 compounds that may be present. In addition, it is inert to the metal salt. It is not a solvent for the metal cyanide catalyst complex that is formed in the reaction of the metal salt and the metal cyanide compound. Preferably, the organic compound is a solvent for the metal cyanide compound and any HwM2(X)6 compounds that may be used. In addition, the organic compound preferably is miscible with the initiator compound that is used in the subsequent alkylene oxide polymerization. Even more preferably, the organic compound is relatively low boiling or otherwise easily separated from the initiator compound.
Thus, suitable organic compounds include polar materials such as, for example, monoalcohols such as methanol, ethanol, n-propanol, isopropanol and the like; polyalcohols such ethylene glycol, diethylene glycol, triethylene glycol, higher polyethylene glycols, glycerine and the like; ethers such as tetrahydrofuran and 1,4-dioxane; ketones such as acetone and methyl ethyl ketone; esters such as methyl acetate and ethyl acetate, nitrites such as acetonitrile, and dimethyl sulfoxide. A preferred organic compound is methanol.
It is preferred to minimize or even eliminate water in the solution of the metal cyanide compound.
The solution of the metal cyanide compound can be prepared in several ways. In one preparation technique, an aqueous solution of the corresponding alkali metal cyanide salt (i.e., Bw[M1(CN)r(X)t], where B represents an alkali metal ion) is formed. This may be performed at a slightly elevated temperature if necessary to dissolve the metal cyanide salt. The aqueous solution is mixed with a slight stoichiometric excess of a concentrated mineral acid of the form HdJ, where J is an anion that forms an insoluble salt with B and d is the absolute value of the valence of J. Common mineral acids such as sulfuric acid and hydrochloric acid are preferred. Sulfuric acid is preferably used at a 75% or higher concentration. Hydrochloric acid is preferably used at a 37% concentration. HCl can also be added by introducing gaseous HCl into the organic compound or by adding a solution of HCl in an appropriate solvent (such as diethyl ether or isopropanol). The salt of B and J precipitates, leaving the desired metal cyanide compound (Hw[M1(CN)r(X)t]) in aqueous solution. The organic compound is then added, usually with stirring, preferably at a slightly elevated temperature in order to maintain the Hw[M1(CN)r(X)t] compound in solution. The salt of B and J separates out from the resulting solution. Because the salt of B and J is usually hygroscopic, a significant portion of the water is removed from the solution with the salt. The salt is easily separated from the supernatant liquid by filtration, centrifuging or other solid-liquid separation technique. If desired, the salt may be washed with additional quantities of the organic compound in order to recover any occluded Hw[M1(CN)r(X)t] compound.
A second method of preparing the solution of the metal cyanide compound is to first form a slurry of the corresponding alkali metal cyanide salt (i.e., Bw[M1(CN)r(X)t]), in a mixture of the organic compound and a stoichiometric excess of a mineral acid, preferably hydrochloric acid. The hydrochloric acid can be supplied in various ways, such as by adding concentrated aqueous HCl, introducing gaseous HCl into the organic compound, or by adding a solution of HCl in an appropriate solvent (such as diethyl ether or isopropanol). An alkali metal salt of the acid forms and precipitates from the solution, leaving the desired Hw[M1(CN)r(X)t] compound dissolved in the organic compound. The precipitate is separated and if desired washed, as before.
A third convenient method of preparing the solution of the metal cyanide compound is by ion exchange. An aqueous solution of the corresponding alkali metal salt (i.e., Bw[M1(CN)r(X)t]) is eluted through a cation exchange resin or membrane which is originally in the hydrogen (H+) form. Sufficient resin is used to provide an excess of H+ ions. Suitable ion exchange resins include commonly available gel or macroporous, crosslinked polystyrene cation exchange resins, such as those sold by The Dow Chemical Company under the trade names DOWEX(copyright) MSC-1, DOWEX(copyright) 50WX4, as well as AMBERLYST(copyright) 15 ion exchange resin, sold by Rohm and Haas. The column is typically eluted with water until the desired metal cyanide compound is recovered. The water is removed from the eluent, yielding the desired metal cyanide compound as solid precipitate. This precipitate is then dissolved or dispersed in the organic compound. If desired, a small amount of water may be left in the metal cyanide compound when it is mixed with the organic compound.
The metal salt is represented by the general formula MxAy. M is preferably a metal ion selected from the group consisting of Zn+2, Fe+2, Co+2, Ni+2, Mo+4, Mo+6, Al+3, V+4, V+5, Sr+2, W+4, W+6, Mn+2, Sn+2, Sn+4, Pb+2, Cu+2, La+3 and Cr+3. M is more preferably Zn+2, Fe+2, Co+2, Ni+2, La+3 and Cr+3. M is most preferably Zn+2.
Suitable anions A include halides such as chloride and bromide, nitrate, sulfate, carbonate, cyanide, oxalate, thiocyanate, isocyanate, perchlorate, isothiocyanate, an alkanesulfonate such as methanesulfonate, an arylenesulfonate such as p-toluenesulfonate, trifluoromethanesulfonate (triflate) and a C1-4 carboxylate. Chloride ion is especially preferred.
Mixtures of two or more metal salts can be used. In such cases, the metals in the metal salt compounds do not have to be the same.
The solution of the metal salt usually can be prepared by directly dissolving the metal salt into an organic compound. The organic compound is as described above. In this solution, the organic compound is preferably the same as used in the metal cyanide compound solution. If a different organic compound is used, it is preferably miscible with that used in the metal cyanide compound solution.
The solutions are mixed in proportions such that at least a stoichiometric amount of the metal salt is provided, based on the amount of metal cyanide compound. Preferably about 1.2 to about 2 equivalents of metal ion (M) are delivered per equivalent of M1(CN)r(X)t ion (or combined equivalents of M1(CN)r(X)t and M2(X)6 ions, when M2(X)6 ions are present). It is preferred that the mixing be done with agitation. Agitation is preferably continued for a period after the mixing is completed. The metal cyanide catalyst, Mb[M1(CN)r(X)t]c M2(X)d, precipitates and forms a fine dispersion in the organic compound.
It has been found that catalyst performance tends to be superior when a excess of metal salt is used. Thus, if only a stoichiometric amount of metal salt is used during the precipitation step, the catalyst can be treated with additional metal salt in a subsequent step.
In the first aspect of the invention, the resulting dispersion is then mixed with an initiator compound. The initiator compound is a material having at least one heteroatom-containing group that will react with an alkylene oxide to form a covalent bond between a carbon atom of the alkylene oxide and the heteroatom, and opening the ring of the alkylene oxide to form a terminal hydroxyl group. The initiator compound is different than the inert organic compound and preferably easily separated therefrom. Suitable initiator compounds are alcohols, thiols (Rxe2x80x94SH compounds) and aliphatic carboxylic acids. The initiator compound may contain as few as one or as many as eight or more such heteroatom-containing groups, depending on the desired nominal functionality of the product polyether. In addition, the initiator compound may contain one or more other functional groups that may be desirable in the product polyether, such as alkenyl or alkynyl unsaturation.
Suitable initiator compounds include monoalcohols such methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, 1-t-butoxy-2-propanol, octanol, octadecanol, 3-butyn-1-ol, 3-butene-1-ol, propargyl alcohol, 2-methyl-2-propanol, 2-methyl-3-butyn-2-ol, 2-methyl-3-butene-2-ol, 3-butyn-1-ol, 3-butene-1-ol and the like. The suitable monoalcohol initiator compounds include halogenated alcohols such as 2-chloroethanol, 2-bromoethanol, 2-chloro-1-propanol, 3-chloro-1-propanol, 3-bromo-1-propanol, 1,3-dichloro-2-propanol, 1-chloro-2-methyl-2-propanol as well as nitroalcohols, keto-alcohols, ester-alcohols, cyanoalcohols, and other inertly substituted alcohols. Suitable polyalcohol initiators include ethylene glycol, propylene glycol, glycerine, 1,1,1-trimethylol propane, 1,1,1-trimethylol ethane, 1,2,3-trihydroxybutane, pentaerythritol, xylitol, arabitol, mannitol, 2,5-dimethyl-3-hexyn-2,5-diol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, sucrose, sorbitol, alkyl glucosides such a methyl glucoside and ethyl glucoside and the like. Low molecular weight polyether polyols, particular those having an equivalent weight of about 350 or less, more preferably about 125-250, are also useful initiator compounds.
At least enough of the dispersion of the metal cyanide catalyst complex is added to the initiator to provide a catalytically effective amount of the catalyst complex in the initiator mixture. Thus, the amount of catalyst complex added is generally at least about 50 ppm, based on the combined weight of the initiator plus catalyst complex, preferably at least about 200 ppm, more preferably at least about 1000 ppm. It is more preferred to form a more concentrated dispersion of the metal catalyst in the initiator. Such a more concentrated dispersion can be divided and/or diluted with additional initiator when it is used to prepare a polyether. Preferably, the concentrated initiator/catalyst complex mixture will contain from about 0.2 weight percent, more preferably from about 0.5 weight percent, most preferably from about 1 weight percent, to about 50 weight percent, preferably about 25 weight percent, more preferably about 10 weight percent, metal catalyst complex, based on the combined weight of metal catalyst complex (as Mb[M1(CN)r(X)t]c[M2(X)6]d.nM3xAy) and initiator.
After the metal catalyst solution and initiator are mixed, the organic compound is removed. The method of accomplishing this will depend somewhat on the particular organic compound and initiator. However, in most cases the organic compound will be more volatile than the initiator, and is conveniently stripped through the application of heat and/or vacuum.
In the second aspect of the invention, the catalyst is precipitated directly in the initiator compound. Separate solutions of the metal cyanide compound and the metal salt (both as described before) are formed in an initiator or mixture of initiators. As before, mixtures of metal cyanide compounds can be used, and an HwM2(X)6 compound can be included if desired. Upon mixing the solutions, the catalyst precipitates to form a catalyst/initiator slurry that can be used directly in making poly(alkylene oxide) polymers and copolymers as described below. In this aspect, an amount of water or organic compound can be mixed into the starting solutions if needed to improve the dissolution of the metal cyanide compound or the metal salt. If water or organic compound is used, it is advantageously stripped from the product slurry as described before.
The resulting product is usually a fine dispersion of the metal cyanide catalyst complex in the initiator. The metal cyanide catalyst complex is present in an active form, and no other treatment or preparation is required. The metal-containing cyanide catalyst can be represented by the general formula:
Mb[M1(CN)(X)t]c[M2(X)6]d.nM3xAy
wherein M, M1, M2, X, A, n, r, t, x and y are all as defined before, M3 is defined the same way as M, b, c and d are numbers that reflect an electrostatically neutral complex, and n is a number indicating the relative number of moles of M3xAy. M3 may be the same or different than M. M3 will be different from M, for example, when a stoichiometric amount of a metal salt MxAy is used in precipitating the catalyst complex, and the precipitated catalyst is then treated with an additional quantity of an M3xAy salt.
Among the catalysts of particular interest are:
Zinc hexacyanocobaltate.nZnCl2;
Zn[Co(CN)5NO].nZnCl2;
Zns[Co(CN)6]o[Fe(CN)5NO]p.nZnCl2 (o, p=positive numbers, s=1.5o+p);
Zns[Co(CN)6]o[Co(NO2)6]p[Fe(CN)5NO]q.nZnCl2 (o, p, q=positive numbers, s=1.5(o+p)+q);
Zinc hexacyanocobaltate.nLaCl3;
Zn[Co(CN)5NO].nLaCl3;
Zn[Co(CN)6]o[Fe(CN)5NO]p.nLaCl3 (o, p=positive numbers, s=1.5o+p);
Zns[Co(CN)6]o[Co(NO2)6]p[Fe(CN)5NO]q.nLaCl3 (o, p, q=positive numbers, s=1.5(o+p)+q);
Zinc hexacyanocobaltate.nCrCl3;
Zn[Co(CN)5NO].nCrCl3;
Zns[Co(CN)6]o[Fe(CN)5NO]p.nCrCl3 (o, p=positive numbers, s=1.5o+p);
Zns[Co(CN)6]o[Co(NO2)6]p[Fe(CN)5NO]q.nCrCl3 (o, p, q=positive numbers, s=1.5(o+p)+q);
Magnesium hexacyanocobaltate.nZnCl2;
Mg[Co(CN)5NO].nZnCl2;
Mgs[Co(CN)6]o[Fe(CN)5NO]p.nZnCl2 (o, p=positive numbers,s=1.5o+p);
Mgs[Co(CN)6]o[Co(NO2)6]p[Fe(CN)5NO]q.nZnCl2 (o, p, q=positive numbers, s=1.5(o+p)+q);
Magnesium hexacyanocobaltate.nLaCl3;
Mg[Co(CN)5NO].nLaCl3;
Mgs[Co(CN)6]o[Fe(CN)5NO]p.nLaCl3 (o, p=positive numbers, s=1.5o+p);
Mgs[Co(CN)6]o[Co(NO2)6]p[Fe(CN)5NO]q.nLaCl3 (o, p, q=positive numbers, s=1.5(o+p)+q);
Magnesium hexacyanocobaltate.nCrCl3;
Mg[Co(CN)5NO].nCrCl3;
Mgs[Co(CN)6]o[Fe(CN)5NO]p.nCrCl3 (o, p=positive numbers, s=1.5o+p);
Mgs[Co(CN)6]o[Co(NO2)6]p[Fe(CN)5NO]q.nCrCl3 (o, p, q=positive numbers, s=1.5(o+p)+q);
as well as the various complexes such as are described at column 3 of U.S. Pat. No. 3,404,109, incorporated herein by reference.
The catalyst complex of the invention is used to polymerize alkylene oxides to make polyethers. In general, the process includes mixing a catalytically effective amount of the catalyst/initiator dispersion with an alkylene oxide under polymerization conditions and allowing the polymerization to proceed until the supply of alkylene oxide is essentially exhausted. The concentration of the catalyst is selected to polymerize the alkylene oxide at a desired rate or within a desired period of time. An amount of catalyst sufficient to provide from about 5 to about 10,000 parts by weight metal cyanide catalyst (calculated as Mb[M1(CN)r(X)t]c[M2(X)6]d.nM3xAy, exclusive of any associated water and initiator) per million parts combined weight of alkylene oxide, and initiator and comonomers, if present. More preferred catalyst levels are from about 20, especially from about 30, to about 5000, more preferably to about 1000 ppm, even more preferably to about 100 ppm, on the same basis.
Among the alkylene oxides that can be polymerized with the catalyst complex of the invention are ethylene oxide, propylene oxide, 1,2-butylene oxide, styrene oxide, and mixtures thereof. Various alkylene oxides can be polymerized sequentially to make block copolymers. More preferably, the alkylene oxide is propylene oxide or a mixture of propylene oxide and ethylene oxide and/or butylene oxide. Especially preferred are propylene oxide alone or a mixture of at least 75 weight % propylene oxide and up to about 25 weight % ethylene oxide.
In addition, monomers that will copolymerize with the alkylene oxide in the presence of the catalyst complex can be used to prepare modified polyether polyols. Such comonomers include oxetanes as described in U.S. Pat. Nos. 3,278,457 and 3,404,109, and anhydrides as described in U.S. Pat. Nos. 5,145,883 and 3,538,043, which yield polyethers and polyester or polyetherester polyols, respectively. Hydroxyalkanoates such as lactic acid, 3-hydroxybutyrate, 3-hydroxyvalerate (and their dimers), lactones and carbon dioxide are examples of other suitable monomers that can be polymerized with the catalyst of the invention.
The polymerization reaction typically proceeds well at temperatures from about 25 to about 150xc2x0 C. or more, preferably from about 80-130xc2x0 C. A convenient polymerization technique involves charging the catalyst dispersion to a reactor and pressurizing the reactor with the alkylene oxide. Polymerization proceeds after a short induction period as indicated by a loss of pressure in the reactor. Once the polymerization has begun, additional alkylene oxide is conveniently fed to the reactor on demand until enough alkylene oxide has been added to produce a polymer of the desired equivalent weight.
Another convenient polymerization technique is a continuous method. In such continuous processes, the activated catalyst/initiator dispersion is continuously fed into a continuous reactor such as a continuously stirred tank reactor (CSTR) or a tubular reactor. A feed of alkylene oxide is introduced into the reactor and the product continuously removed.
The catalyst of this invention is especially useful in making propylene oxide homopolymers and random copolymers of propylene oxide and up to about 15 weight percent ethylene oxide (based on all monomers). The polymers of particular interest have a hydroxyl equivalent weight of from about 800, preferably from about 1000, to about 5000, preferably about 4000, more preferably to about 2500, and unsaturation of no more than 0.02 meq/g, preferably no more than about 0.01 meq/g.
The product polymer may have various uses, depending on its molecular weight, equivalent weight, functionality and the presence of any functional groups. Polyether polyols so made are useful as raw materials for making polyurethanes. Polyethers can also be used as surfactants, hydraulic fluids, as raw materials for making surfactants and as starting materials for making aminated polyethers, among other uses.